Manufacture of springs

ABSTRACT

Low temperature heat treatment of springs after coiling is achieved by passing the springs, individually on a conveyor moving at a steady speed, through a heating chamber in the form of an elongate tunnel. Radiant heating means rapidly heats the springs as they are carried through the heating chamber so that they undergo a desired heat treatment. Means may be provided whereby springs can be heated at different rates as they pass through different parts of the heating chamber, so as to afford improved control of the heat treatment.

[22] Filed:

United States stem [191 Quarmby et al.

[ MANUFACTURE OF SPRINGS [75] Inventors: Robert Charles Quarmby; Terence James Leonard Clarke, both of Groby, Leicestershire; Barry Charles Thomas Wright, Birstall, Leicestershire, all of England [73] Assignee: The British United Shoe Machinery Company Limited, Leicester,

England June 14, 1972 [21] Appl. No.: 262,456

[52] US. Cl..., 219/388, 219/352, 219/411, 219/553, 34/207 [51] Int: Cl. F271) 9/06 [58] Field of Search 219/352, 354, 388, 219/411, 553; 34/203, 207

[56] I References Cited UNITED STATES PATENTS 2,504,110 4/1950 Davis et a1. 219/388 2,954,826 10/1960 Sievers 219/354 X 3,249,741 5/1966 Mills 219/388 3,601,582 8/1971 DeBoisfleury 219/388 3,304,406 2/1967 King 219/411 3,626,154 12/1971 Reed r 219/411 3,697,722 10/1972 Fumicln 219/388 X FOREIGN PATENTS OR APPLICATICNS 69,149 4/1958 France 219/354 693,878 7/1953 Great Britain 219/388 Primary Examiner-Velodymyr Y. Mayewsky AttorneyWil1iam R. Evans et a1.

[57] ABSTRACT Low temperature heat treatment of springs after coiling is achieved by passing the springs, individually on a conveyor moving at a steady speed, through a heating chamber in the form of an elongate tunnel. Radiant heating means rapidly heats the springs as they are carried through the heating chamber so that they undergo a desired heat treatment. Means may be provided whereby springs can be heated at different rates as they pass through different parts of the heating chamber, so as to afford improved control of the heat treatment.

2 Claims, 6 Drawing Figures PATENIEDnm 15 1975 SHEET 5 OF 5 MANUFACTURE OF SPRINGS BACKGROUND OF THE INVENTION In the manufacture of coil springs from wire, which may for example be patented hard-drawn steel wire, it is a common practice to subject springs formed in a coiling operation to low temperature heat treatment whereby undesirable stresses set up in the springs during the coiling operation can be relieved and mechanical properties of the springs improved.

Apparatus commonly employed in such heat treatment comprises an oven in which batches of springs are placed in baskets in the oven. Such an oven may be maintained, for example, at a temperature of about 225 C and the springs left in the oven for about 30 minutes. Such known methods of spring heat treatment, though satisfactory for batch production of springs, is not particularly suitable for production-line manufacture, in which springs are conveyed one at a time from a coiling station, at which they are coiled on a coiling machine, and through several working stations at which various operations may be performed on the springs (for example, heat treatment, grinding, looping, pre-stressing) to produce a finished spring ready for packaging. A further disadvantage of such known methods of heat treatment is that the springs in a basket do not all receive the same heat treatment, as those on the outside are heated more quickly than those towards the middle of the batch.

SUMMARY OF THE INVENTION In view of the foregoing it is an object of this invention to provide spring heat treatment apparatus that is suitable for incorporation in automatic plant for production-line manufacture of springs.

To this end and in accordance with a feature of the invention, apparatus is provided that comprises a housing that provides a heating chamber in the form of an elongate tunnel, conveyor means arranged to carry springs individually through the heating chamber, and radiant heating means arranged to heat, by radiant heat, springs passing through the heating chamber on the conveyor means so that the springs undergo a desired heat treatment. In a preferred form of apparatus according to the invention, the radiant heating means comprises radiant heating units body portions of which together define a substantially cylindrical heating chamber the body portions of the radiant heating units may be of a refractory material and of part-cylindrical form, with electric heating elements embedded in the body portions by which the body portions can be heated. Preferably also adjustment means is provided whereby the alignment of the conveyor means in the BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other features of the invention will now be more particularly described in connection with two illustrative embodiments and with reference to the accompanying drawings in which FIG. I is a perspective view of the first illustrative apparatus, with part of a housing of the apparatus broken away to reveal radiant heating units of the apparatus;

FIG. 2 is an end elevational view of the first illustrative apparatus;

FIG. 3 is a perspective view of the second illustrative apparatus with a housing of the apparatus shown opened to reveal radiant heating units of the apparatus;

FIG. 4 is a view in elevation of one end of a housing of the second illustrative apparatus, shown with an end plate of the housing removed;

FIG. 5 is a view in plan of pulley meansof the second illustrative apparatus, located at the far end of the apparatus as shown in FIG. I; and

FIG. 6 is a view in perspective illustrating an alternative form of housing suitable for use in an apparatus according to the invention.

The first and second illustrative methods of heat treatment are methods of low temperature heat treatment of cylindrical compression springs coiled from patented hard drawn wire, whereby stresses in the springs can be relieved and mechanical properties of the springs improved. The first illustrative apparatus is suitable for use in carrying out the first illustrative method and is illustrated in FIGS. 1 and 2. The first illustrative apparatus comprises an elongate cylindrical housing i2 within which is provided a heating chamber. A cylindrical outer wall 14 of the housing 12 is of metal and is coated on an inner surface 15 thereof with a layer of gold. A cylindrical inner wall 18 of the housing 12 is of quartz that is substantially transparent to radiant heat and is held coaxial with the wall 14 by annular end plates 20. Secured to the inner surface 15 of the cylindrical outer wall 14, in the annular space between the inner and outer walls and uniformly spaced around the longitudinal axis of the wall 14 in a cylindrical formation, are eight electric radiant heating units 22 of radiant heating means'of the first illustrative apparatus. In

use of the first illustrative apparatus, energy is radiated from the units 22 and directed towards the longitudinal axis of the housing 12, the layer of gold on the inner surface 15 of the outer wall 14 providing a highly reflective surface. Cooling fluid is supplied through a pipe 24 into the space between the outer and inner walls 14 and 18 respectively, and through a pipe 26 back to the cooling device, whereby overheating of the apparatus is controlled.

The first illustrative apparatus also comprises conveyor means, indicated generally at 30, adapted to convey a spring at a steady speed through the heating chamber. The conveyor means comprises two mutually inclined endless open mesh web belts 32, each belt extending through the housing 12 (see FIG. 1) between two adjacent rollers 34 located at one end of the housing 12 and two adjacent rollers 36 located at the other end of the housing 12. An axis of rotation of each roller 34 is inclined to the axis of rotation of the other roller 34, both axes lying in a plane normal to the longitudinal axis of the housing 12. Similarly the axis of rotation of each roller 36 is inclined to the axis of rotation of the other roller 36, both axes lying in a plane normal to the longitudinal axis of the housing 12, (see FIG. 2). The two web belts 32 thus provide a conveyor belt 33 of V- section, a plane bisecting the angle between the axes of rotation of the rollers 36 (and the rollers 3d) passing through the longitudinal axis of the housing l2, (see FIG. 2). The housing 12 is mounted on vertical support columns 50 with adjustment means to enable heightwise adjustment relative to the conveyor means 30. Thus the alignment of the conveyor means in the heating chamber can be varied so that for springs of different size a spring can be carried through the heating chamber substantially centrally of the heating chamber; a cylindrical spring on the conveyor means 30 is thus maintained, as it is conveyed through the housing, coaxial with the housing 112.

In use of the first illustrative apparatus, in accordance with the first illustrative method, springs are conveyed through the heating chamber within the housing, which is 16 inches long, at a speed of 2 inches per second. The position of the housing 12 on the support columns 50 is adjusted so that springs on the conveyor means 30 are maintained coaxial with the housing 12 as they pass through the heating chamber. As the springs pass through the heating chamber they are heated by the radiant heating units 22 of the radiant heating means so that they become heated. The electric power supplied to the heating units 22 is adjusted so that springs passing through the heating chamber are heated to a required degree so as to undergo a desired heat treatment. In the first illustrative method the springs were heated to a maximum temperature of 260 In FIGS. 3, 4 and 5 is illustrated the second illustrative apparatus which is adapted for use in accordance with the second illustrative method. The second illustrative apparatus comprises conveyor means 110 for transporting a coil spring S at a steady speed through a cylindrical heating chamber 112 of the apparatus (best seen in FIG. 4). The conveyor means 110 comprises two endless steel belts llld which are mounted side-by-side, spaced apart, to extend in an elongate loop between a single pulley wheel lllfi at one end of the loop and two pulley wheels lib at the other end of the loop. The pulley wheels 1w are mounted for rotation about horizontal axes. The belts HM extend between the pulley wheels 1lll6 and H8 horizontally and parallel to one another, through guides 115. The pulley wheel llld is rotatably mounted on a bearing block 120, and is arranged to be rotated by an electric motor 122 by way of a reduction gearbox 12d. Axles I23 extending from the pulley wheels ll 18 are rotatably supported on carriages .1126. The carriages 1126 (as best seen in FIG. 5) are independently mounted for sliding movement in a direction parallel to the direction of extension of the belts lllld between the pulley wheels 116 and 118, and are urged by springs I27 away from the hearing block 120; the belts 11114 are thus maintained constantly in tension by the springs 127. Screw means 129 is provided whereby the tensioning force exerted by the springs 127 can be varied.

The conveyor means 110 of the second illustrative apparatus is arranged in relation to the heating chamber 1112 so that one length of the belts l M between the pulley wheels H116 and H18 extends through the chamher and the other length extends outside, beneath the chamber.

The second illustrative apparatus comprises a housing 12% (lFIGS. 3 and 41) within which are mounted three heating groups of four part-cylindrical electric radiant heating units 330 of radiant heating means of the apparatus, each group of four units 130 being arranged in a cylindrical formation and the three groups of units being arranged coaxially to define the cylindrical heating chamber 1112. The heating units 130 are commercially available in the United Kingdom under the trade name Elstein, each unit being rated at 240 volts and 1,000 watts and having a body portion of a refractory material with an electric heating element embedded in the body portion. On connection of the heating element to a source of electric power the element and the body portion become heated so that energy is radiated from the heating unit. Insulation material is packed between the units and outer walls 131 of the housing 128 to reduce heat loss and avoid overheating of the housing 128. Means is provided for controlling the electric power supply to each of the three groups of heating units 130 so that the operating temperatures of the three groups can be individually controlled. Temperatures in the tunnel are gauged by means of thermocouple devices 132.

In use of the second illustrative apparatus in accordance with the second illustrative method the belts 1M carry a cylindrical compression coil spring S, the spring belt being supported between the belts on inside edge portions of the belts, through the heating chamber 112, operation of the electric motor 122 driving'the' pulley wheel 116 and hence the belts 114. The belts 1M and the chamber 112 are so arranged that the springs is maintained, as it passes through the chamber, coaxial with the chamber. As the spring is passed through the heating chamber it is subjected to the heating effect of theradiant heating means. Each of the three heating unit groups defines a heating zone of the heating chamber, the temperature at which the units of any one group are maintained determining the rate at which the spring is heated while in that particular zone. The heating chamber thus comprises a plurality of heating zones in which in use of the apparatus a spring can be heated at different rates while passing through the heating chamber. In the second illustrative method the second llustrative apparatus is arranged so that a spring transported at a steady speed through the heating chamber 112 is heated rapidly in a first heating zone provided by the first two heating groups through which it passes, to a temperature approaching a desired final spring temperature, and is then heated, at a lower rate of heating than in the first heating zone, in a second heating zone, provided by the third heating group alone, up to the desired final spring temperature; in this way the temperature of the spring can in a controlled manner be accurately raised to the desired final value.

It will be appreciated that although in use of the second illustrative apparatus according to the second illustrative method, the first and second groups of heating units are maintained at the same operating temperatures, in other methods according to the invention the heating unit groups might be maintained at different temperatures. I

In FIG. 6 there is illustrated a further form or housing suitable for use in an apparatus according to the invention. Th housing is provided by cast sections 136 of a refractory ceramic, material available in the U.K. under the trade name Veriform. The sections 1136 are cast in pairs, each pair of sections together constituting a modular housing block 113%. Each section 136 provides two dovetail guideways M0 in which mounting portions 141 of part-cylindrical electric radiant heating placed end to end (two shown in FIG. 6) so that an 5 elongate, substantially cylindrical, heating chamber is provided. In similar manner to that of either the first or the second illustrative apparatus, conveyor means can be arranged to convey a spring through the heating chamber provided by blocks 138, each block providing a heating zone. The temperature of the heating units 142 of each block 138 may be controlled independently of the units in the other blocks 138 so that a spring can be heated at different rates in different zones as it passes through the heating chamber.

Having thus described our invention, what we claim as new and desire to secure by Letters Patent of the United States is:

1. A spring heat treating apparatus comprising: a thermally insulating housing which provides an elongate, open-ended chamber; a conveyor having two endless, spaced-apart, parallel belts each extending between pulley wheels and through the chamber in a direction parallel to and equidistant from a longitudinal axis of the chamber; a plurality of electrical radiant heating units mounted on the housing within the chamber equidistant from the longitudinal axis of the chamber, each radiant heating unit being of part cylindrical form and units being arranged to define a substantially cylindrical heating chamber; and drive means for driving the two endless belts along their lengths at the same constant speed to carry a spring supported between the belts at constant speed along the longitudinal axis of the chamber to heat the spring with the radiant heating units.

2. Apparatus according to claim 1 in which the radiant heating units are grouped along the longitudinal axis of the chamber to define heating zones along the chamber for heating a spring at different rates in the different heating zones as it is carried along the chamber. 

1. A spring heat treating apparatus comprising: a thermally insulating housing which provides an elongate, open-ended chamber; a conveyor having two endless, spaced-apart, parallel belts each extending between pulley wheels and through the chamber in a direction parallel to and equidistant from a longitudinal axis of the chamber; a plurality of electrical radiant heating units mounted on the housing within the chamber equidistant from the longitudinal axis of the chamber, each radiant heating unit being of part cylindrical form and units being arranged to define a substantially cylindrical heating chamber; and drive means for driving the two endless belts along their lengths at the same constant speed to carry a spring supported between the belts at constant speed along the longitudinal axis of the chamber to heat the spring with the radiant heating units.
 2. Apparatus according to claim 1 in which the radiant heating units are grouped along the longitudinal axis of the chamber to define heating zones along the chamber for heating a spring at different rates in the different heating zones as it is carried along the chamber. 